The invention relates to devices which control the rate of descent of any person who is supported by a rope, but in particular, to a mountain climber.
Mountain climbers commonly descend a mountain by rappelling. In this method, the climber attaches a support rope or pair of ropes to a natural feature such as a tree or rock out-crop which serve as an anchor or alternatively, to an artificial anchor implanted in the mountain. The climber then descends the mountain supported by the anchored support rope(s). The support rope is looped around or through the anchor in a manner so that two rope strands pass through a descending device which is attached to the climber's harness. After the rappel is completed, the rope may be retrieved by pulling on one of the rope strands.
The device commonly used as a rope descender is known as a Figure Eight. As shown in FIG. 1, the Figure Eight 2 consists of a pair of rings, 3, 4, integrally connected by a neck 5. The upper ring 3, through which the support rope is passed, is considerably larger in diameter than the lower ring 4 which serves as a carabiner hole to which a carabiner is attached for connection to the harness of the climber. As shown in FIG. 2, the support rope 24 is attached to the Figure Eight by passing a loop of the support rope through the large hole 6 of the upper ring 3 and then pulling it over and then under the lower ring 4 so that the rope is secured around the neck of the Figure Eight. One end of the loop 26 remains connected to the anchor whereas the free end of the rope 28 is looped around the Figure Eight and is grasped by the climber to control his rate of descent. The major factor in controlling the climber's rate of descent is the amount of friction of the rope with the descending device. In the Figure Eight, the amount of such friction is determined by the size of the rope used as this alone will determine the area of surface contact between the rope and the Figure Eight.
Use of the Figure Eight presents several problems. When the mountain climber is doing multiple rappels, the Figure Eight must be removed from the climber to reattach the rope since the free end of the rope is looped around the Figure Eight. This procedure presents a safety risk because the climber is opening his connection to the anchor to remove the Figure Eight.
Another disadvantage of the conventional Figure Eight is that the support rope occasionally slips from the neck and slides to the top of the upper ring, thereby interlocking with the length of support rope extending to the anchor, and stopping the climber's descent until the accidental locking can be undone. To avoid this problem, some Figure Eights are provided with ears which prevent such rope slippage.
A further disadvantage of the Figure Eight is that it does not work well when the support rope is frozen because of the sharp turns the rope takes while passing through the descending device during rappel.
Another disadvantage is that the Figure Eight only provides one friction level to control the rate of descent - that defined by the number and diameter of the rope(s) used, and the condition of the rope, i.e., whether the rope is wet, dry or frozen.
One attempt to overcome one of the problems of the Figure Eight by giving the climber additional control over the amount of friction is a carabiner attachment known commercially as the SMC Brake Bar manufactured by Seattle Manufacturing Company. This brake bar is pivotally attached to a side of the carabiner and may be positioned across the inner aperture of the carabiner. The support rope is looped over the brake bar to increase friction. This device has a safety problem because it loads a single carabiner at its weakest point, the pivot point of the bar. Further, the device provides only a marginal increase of friction because only one brake bar can be used.
Another method of controlling a climber's rate of descent is known as a carabiner brake which is an assembly consisting entirely of carabiners. In this method, two carabiners functioning as a brake, circumscribe the middle of two other carabiners which serve as a frame and the support rope is looped therein. A carabiner connects the carabiner frame to the climber. A major disadvantage of this method is that the lack of a solid descender body poses a safety hazard. A further disadvantage is that assembly of the carabiner brake is time-consuming and cumbersome, disadvantages which are magnified when a mountain climber is doing multiple rappels in storm conditions.